The present invention relates generally to motion control systems and in particular, to a multi-axes, positioner having sub-micron resolution.
Motion control technology requires precision, speed and accuracy. Several years ago, systems able to position to 10 micro inches (10 millionths of an inch) were considered state-of-the-art. Mechanical limits of current motion control designs, however, inhibit the ability to provide precise, quick and accurate positioning in the nanometer and sub-nanometer range. Nevertheless, today companies routinely require the ability to position to fractions of a micron for such applications as semiconductor tool design, disk-drive testing, fiber-optics equipment, lithography, line-width metrology and nanometer-scale development to name a few.
Today's motion control systems are made up of a number of components that typically include one or more stages, drive mechanisms, encoders and control electronics. A stage is a mechanical device that produces a linear translation, either by conversion of rotary motion or by linear motors directly. It typically consists of three main components: a stationary member or base, a moving member, and a carriage, which generally includes bearings. The base is designed to support a load and carry the bearings on which the carriage travels. The carriage is attached to the drive mechanism, which causes it to move along the base. Several mechanical and electrical types of drive mechanisms exist. These include manual, pneumatic, hydraulic, rack and pinion, lead screw, belt and pulleys, linear type motors (cog-free, iron core, DC brushed servo motors and linear steppers), voice coils, and rotary type stepper or servomotors.
While such drive mechanisms are adequate for coarse positioning, they are typically not suited for positioning that requires fine, accurate and fast movement. A piezoelectric motor-driven stage is often used on top of a pre-existing stage to provide for such movement. Piezoelectric motors have many advantages over conventional magnetic motors. These advantages include high precision, repeatable nanometer and sub nanometer-size steps, quick response (they are one of the fastest responding positioning elements currently available), and no wear and tear because of their solid-state structure. Thus, by combining the use of a magnetic motor-driven stage with a piezoelectric motor-driven stage, the motion control system can move with the former into a coarse position to achieve long travels, and then with the latter for final sub-nanometer moves.
The use of stacked stages, however, presents problems. Not only does such stacking add to the height of the system, but it's cost as well. As the height of the system increases, so does the risk of vibration, which reduces the accuracy and precision of the system. This problem is exacerbated in the case of dual-axis systems that require two times the height of single axis systems. Moreover, stacked stages increase the risk of abby errors (i.e., rolling, pitching and yawing). Further, in some applications when extremely straight motion or multi-axis motion is required, stacked stages alone are not sufficient to perform complex tasks.
As a result, there is a need for a cost-effective, multi-axes, single story positioner that provides for fine positioning in the sub-micron range.